When it comes to advising their executors, even the most posterity-minded writers can fall short of being comprehensive. David Foster Wallace left a manuscript bathed in lamplight in the garage where he worked and so the publication last year of The Pale King: an Unfinished Novel, could be seen as a fulfilment of the author’s wishes or at least as an exercise conducted in basic accordance with them. If Both Flesh and Not can’t exactly be called a violation, then that is only because it wouldn’t have occurred to Wallace to leave instructions such as “Don’t put between hard covers articles I have chosen to omit from both of my essay collections,” or: “As for my book-of-the-year selection from 1994, I’m happy for it to languish in Spin magazine, there for scholars, librarians and diehard fans to unearth. Nobody should have to pay for that.”

The book of the year in question was Zbigniew Herbert’s poetry collection Mr Cogito and now, in a book subtitled “Essays”, Wallace’s few hundred words about the book exist for posterity under the title “Mr Cogito”, as if this were intended to be his enduring account of the book in the way that the several-thousand-word rumination “Joseph Frank’s Dostoevsky” (from Consider the Lobster and Other Essays) was intended as his enduring account of Joseph Frank’s Dostoevsky – the first four volumes, anyway.

While there is nothing here that reflects very badly on Wallace or that reveals him as anything other than the energetically grappling, genuinely curious, unabashedly didactic, agonisedly self-conscious, approval-hungry, frequently exhilarating and just as often muddled thinker revealed by the collections he presided over himself, it is nevertheless a shame that there now exists in book form evidence of Wallace as a practitioner of modest journalistic undertakings, as well as of mammoth tasks such as the cruise ship holiday that provided the title piece for his first collection, A Supposedly Fun Thing I’ll Never Do Again, and the lobster festival visit that provided the title piece for his second, Consider the Lobster.

When Wallace killed himself in 2008, less than three years had passed since the publication of this latter book. It might be said that his preferred period of gestation was around a decade, if we take the time that elapsed between his first piece of journalism and Collection No 1 and between Collection No 1 and No 2 as the beginnings of a pattern. When it came to sifting through his journalism for Collection No 2, Wallace chose to include nothing that could have made it into the earlier book but didn’t. Roberto Bolaño probably wouldn’t have published his hard drive if given the choice and John Lennon might not have published his shopping lists but there was no clear precedent for the taking of those decisions. Wallace had shown how he wanted his non-fiction to be treated and it didn’t involve the conversion of ephemera into filler.

In other words, if Wallace had survived long enough to preside over a further collection, it is unlikely it would have looked like this. Both Flesh and Not is a mopping-up exercise of the kind that scholars might undertake some time after the death of a writer who had made a large number of choices pertaining to preservation during his life, such as From the Uncollected Edmund Wilson or E B White’s Writings From the New Yorker 1927-76. It is not a genuine sequel, as the posthumously edited and assembled Higher Gossip was to a large degree a genuine sequel, in terms of presentation and the criteria for inclusion, to earlier collections of John Updike’s essays such as Odd Jobs and More Matter.

The new book also complicates the chronological trajectory traced in the previous col - lections, whereby Wallace could be seen moving ever closer to a belief in fiction as a mode of “deep conviction” rather than “ironic distance” – though, as this book displays, his taste for deflection was consistently strong: “There’s a marvellously apposite Heidegger quotation here, but I’ll spare you”; “Marx (sorry – last dropped name)”; “Whatever that’s supposed to be mean”; “Whatever ‘ego’ means”; “Your guess here is probably as good as anyone’s.”

Wallace had written at least two things that he would probably have wanted to collect, though one of them, the commencement address he delivered at Kenyon College in 2005, has already been published as This Is Water. The other, “Federer Both Flesh and Not”, is paid the double compliment of serving both as the collection’s opening essay and the source of its title. It is an unsympathetic piece of work, mechanical in its appreciation of Federer’s style and credulous in its reading of his character. Wallace wrote more enlighteningly about tennis in the opening essay of A Supposedly Fun Thing I’ll Never Do Again, in which he connects his success as a junior and his “jones for mathematics” to the topographic make-up of the Midwest, and in the essay about the American player Michael Joyce, in which his reflections on the modern game were less exalted and more convincing. In the Federer piece, he sometimes forgets that his readers might have watched some tennis and even developed views about it. “The thing about the ball cooperatively hanging there, slowing down, as if susceptible to the Swiss’s will – there’s real metaphysical truth here,” he writes. The sentence is typical of his weakness for both aggrandisement and self-aggrandisement, the praise of Federer being indistinguishable from implicit praise of his own powers of perception and divination.

Neither of the two other pieces written since Consider the Lobster – “Deciderization 2007: a Special Report”, on guest-editing The Best American Essays, and “Just Asking”, a series of rhetorical questions that amount to an argument for freedom over security – could be called negligible. Yet it is easy to imagine Wallace choosing not to collect them, as he had already done with so much of the stuff here – such as the long review of Edwin Williamson’s Borges: a Life (“Borges on the Couch”), which ran in the New York Times in 2004, or the prose poem about prose poetry, or the essay on “conspicuously young” writers, which contains the words: “As of this writing, late 1987”. He presumably thought that the latter essay, which contains a section about television, had been superseded by the even longer and more searching “E Unibus Pluram: Television and US Fiction”. Now, in the interests of completism or commerce, we have it, along with the admission, in the acknowledgments pages, that some of the “ideas and language” in “Fictional Futures and the Conspicuously Young” recur in “E Unibus Pluram”.

A more perverse act of mummification occurs in the selections from Wallace’s “vocabulary list” – “words that he wanted to learn” – printed before each essay. In the earlier books, Wallace’s word-learning emerges in his writing – you come across “glabrous”, “anaclitic”, “lallating”, “decocted”. Nobody ever thought that Wallace was a natural writer or that he didn’t work to be, in Benjamin Markovits’s phrase, “at the same time . . . a nerd and a dude”; you only have to see him use the phrase “hellaciously un-fun” on the Charlie Rose show or to read Jonathan Franzen’s astonishingly unguarded essay “Farther Away” to know that he was engaged in a permanent process of image-projecting, as well as an accompanying process of concealment. Evidence of preparatory work such as the word lists have no place in a book solely attributed to David Foster Wallace.

Wallace’s non-fiction looks doomed to suffer as a result of posthumous manoeuvres, at least in the short term. Both Flesh and Not is damaged by the memory of its putative predecessors – one word note disparages a noun, “pulchritude”, that he used in A Supposedly Fun Thing – but all of his non-fiction has been compromised or overcast by the revelations in D T Max’s trim biography Every Love Story Is a Ghost Story. (The titles of the collection and the biography, as well as Wallace’s best-known novel, Infinite Jest, enact a collision of the metaphysical and the sensual or corporeal, as the titles of film portrayals of Bob Dylan – Dont Look Back, No Direction Home, I’m Not There – all contain negatives.) We know too much and might find it hard to take all of Wallace’s pronouncements at face value, as detached or disinterested.

How, for example, to approach the apparently systematic essay on conspicuously young writers when we know that, in Max’s words, “He eyed the output of his contemporaries with envy,” or that reading William Vollmann, “He felt a familiar twinge of envy and anger”? Wallace’s intemperate loathing of Updike’s lasciviousness now looks like a straightforward if veiled case of self-loathing and the final line of the Updike essay like veiled self-portraiture: “It never once occurs to him, though, that the reason he’s so unhappy is that he’s an asshole.” It is impossible, having learned so much about Wallace’s upbringing, to locate anything besides darkness and misery in his confession that during his Midwest childhood, he had “this weird, deluded but unshakable conviction that everything around me existed all and only For Me”.

A moment in one of the more substantial pieces in Both Flesh and Not, “Borges on the Couch”, now looks less like a piece of rigorous criticism than an act of denial and deception, not to mention unscrupulous disparagement. Literary biographers are often attacked for trying to plumb the depths of both literature and human beings. But the reader who, as Max reveals, wrote his mother’s initials next to the sentence (in an Alice Miller book) “As soon as the child is regarded as a possession for which one has a particular goal . . . his vital growth will be violently interrupted” might have found it comforting, when reading that Borges’s mother “induced a sense of unworthiness” in her son by urging him “to realise the ambitions she had defined for herself”, to reject the plausibility of such a claim and advise his genuflecting readership: “[M]uch of the mom-based psychologising seems right out of Oprah.”